There are many different types of water meters, all using different principles to measure water flow including positive displacement, multi-jet, nutating disc, and the fluidic oscillator, just to name a few. Although they utilize vastly different principles to measure flow, the principle used to test their accuracy is the same: run an absolute known volume of water through a meter or group of meters, and compare their registered volumes to that of the known volume. If the results show an acceptable deviation from the known volume, then the meter is working correctly, if the deviation is unacceptable, it is not.
Further, while meters may be the exact same make and type, the results they produce can be entirely different. For example, some meters may not be accurate on low flows, others on high flows.
When testing flow meter accuracy, one should remember that the accuracies of the tests are only as good as the accuracy to which the meters are read. The most widely used and probably the most popular method for testing meters is the volumetric system. The volumetric system can be compared to a measuring cup; the system tanks are calibrated and volumes are marked at different levels along the side, and the water level is viewed through a sight tube. The test fluid is pumped through the meters under test and into the storage tanks and the corresponding volume is then compared to the volumes recorded by the meters.
Another fluid meter test system is the gravimetric test system. The standard prior art gravimetric test system is made up of the following components:                Test Bench: The actual device on which meters are placed, secured, and read;        Control Console: The testing interface which houses the control wiring, computer, and scale interface hardware;        Scales: The physical hardware on which the measurement tank(s) sit that measures the weight of the water inside the measurement tank(s);        Controller: The measurement system used to measure volume and serve as an operator interface for the computerized and manually controlled tests;        Software: The software used in conjunction with the Controller to control and document the tests as well as provide an inventory database;        Measurement Tanks: Tanks to which water is directed for measuring volumes via the scales;        Control Valves: A system of valves that direct the water throughout the different cycles of testing;        Motion Operator: The device on the test bench, which pushes the valves and spools together, making a water tight transition from meter to meter without using bolts;        Test Spools: Varying lengths and diameters of pipe spools used as spacers and transition pieces between meters;        Carrier Bars: The device on the bench that holds the meters in place, allowing them to slide while the clamping device pushes them together, without the need for bolts;        Roto Meters: Quick reference flow meters allowing the technician to set an approximate flow (to within + or −2%) rate while running a test;        Meter Adaptors: Used for positioning MNPT threaded meters to provide for the transition from one meter size to the next;        Electric Actuator: The part of the motion operator that moves the device.        
One short coming of prior art gravimeter systems is that they require different size tanks for different flow rates with each tank having its own scale. Such test systems may require a 3,300-gallon tank and associated scale, a 100-gallon tank and associated scale, and a 10 gallon tank and associated scale. Such tank systems require lots of room and redundant scale technology. What is needed is a way of reducing the number of different tank and associated scale structures.
Another problem with prior art test systems is that they were designed for metal meters. Consequently, the test system meter interface (e.g. meter fitting), used to associated the meter under test with the test bench, is configured for metal meters. Today, flow meters are increasingly being manufactured from composite materials and plastics. While such test systems can still be used to test composite meters, the prior art meter interface places (and associated clamping forces) significant stresses on a plastic meter and if one is not careful such a meter can be deformed affecting its accuracy during the test. Further, such stresses may cause permanent damage. What is needed is a new meter interface that does not subject the meter under test to unacceptable levels of pressure and stress.
Yet another shortcoming of prior art test system is that they are not well suited to test multiple fire hydrant meters. Novel support structures that stabilize large meters are disclosed.
Yet another shortcoming of prior art test systems is that the meter clamping process is riskier than it need be for larger meters.
Yet another shortcoming of prior art test systems is that they are not setup to test ultra low flow meters.
The disclosed inventions address at least the above described shortcomings.